Verbose output for Be and BeExactly string comparison

Adding verbose output when comparing strings with Be or BeExactly to make spotting the difference between the strings easy. Also replacing non-printable characters such as new line or tab with escape sequences (e.g. ```\t```) 

```powershell
describe "Special output for string in Should Be" {
    it "outputs verbose message" {
        "abc" | Should Be  "abd"
    }
    
    it "outputs verbose message" {
        "A" | Should BeExactly "a"
    }
    
    it "outputs verbose message" {
        "Nothing." | Should Be "At least something."
    }
    
    it "outputs verbose message with special characters replaced" {
        "TABBED`t
NEWLINE." | Should Be "Something else."
    }
}
```
```
Describing Special output for string in Should Be
 [-] outputs verbose message 162ms
   String lengths are both 3. Strings differ at index 2.
   Expected: {abd}
   But was:  {abc}
   -------------^
   at line: 3 in C:\temp\VerboseOutputExamples.ps1
 [-] outputs verbose message 16ms
   String lengths are both 1. Strings differ at index 0.
   Expected: {a}
   But was:  {A}
   -----------^
   at line: 7 in C:\temp\VerboseOutputExamples.ps1
 [-] outputs verbose message 15ms
   Expected string length 19 but was 8. Strings differ at index 0.
   Expected: {At least something.}
   But was:  {Nothing.}
   -----------^
   at line: 11 in C:\temp\VerboseOutputExamples.ps1
 [-] outputs verbose message with special characters replaced 12ms
   Expected string length 15 but was 17. Strings differ at index 0.
   Expected: {Something else.}
   But was:  {TABBED\t\r\nNEWLINE.}
   -----------^
   at line: 16 in C:\temp\VerboseOutputExamples.ps1
```